1. Field of the Invention
The present invention relates to a transflective liquid crystal display device that can be used in both transmissive and reflective modes and a method for manufacturing the same.
2. Prior Art
Transflective liquid crystal display devices, which operate in a reflective mode utilizing ambient light in bright places and operate in a transmissive mode utilizing backlight in dark places, are broadly used, in particular, as display devices in portable electronic equipment. For example, Japanese Unexamined Patent Publication No. H10-282488 entitled “Liquid crystal display device” proposes a liquid crystal display device in which holes for transmitting light are provided on a reflective layer of a reflective liquid crystal display device and, at the same time, a backlight device is provided behind the reflective layer. When this device is used in the reflective mode, an image is displayed by the ambient light reflected by the reflective layer disposed behind a liquid crystal layer and, when this device is used in the transmissive mode, the image is displayed by guiding the light from the backlight device to the liquid crystal cell through the holes provided on the reflective layer.
However, the device disclosed in Japanese Unexamined Patent Publication No. H10-282488 has a problem in that, in a color display mode, color reproducibility is not optimized in both the reflective mode and the transmissive mode. The reason of this problem is as follows. When the device is used in the reflective mode, the ambient light passes through the liquid crystal layer and a color filter and is reflected by the reflective layer disposed on the backside of the color filter and, then, passes through the color filter and the liquid crystal cell again and, then, exits from the cell and is observed by a user. Therefore, as the incident light passes through the color filter twice before exiting from the cell, the transmittance of the light and, thus, the brightness of the display is reduced by the color filter. As the light passes through the color filter twice, the color saturation of the light is increased. In contrast to this, when the device is used in the transmissive mode, as the light that is originated from the backlight device disposed behind the cell passes through the holes disposed on the reflective layer and, then, passes through the color filter and liquid crystal cell and exits from the cell, the light passes through the color filter only once. Therefore, the brightness of the display is not reduced but the color saturation is reduced. As described above, as the color reproducibility is not optimized in both the transmissive mode and the reflective mode, there is a problem in that, if the optical density of the color filter is optimized for either the transmitting mode or the reflective mode, the display in the other mode is not optimized.
In order to solve the above problem of the liquid crystal display device shown in Japanese Unexamined Patent Publication No. H10-282488, other liquid crystal display devices have been proposed in Japanese Unexamined Patent Publication No. 2000-298271 entitled “Liquid crystal display element and method for manufacturing the same”, Japanese Unexamined Patent Publication No. 2001-33778 entitled “Liquid crystal display device and method for manufacturing the same and electronic equipment” and the like. As these liquid display devices are configured so that the thickness of the color filter differs between the region above a reflective layer and the region above openings of the reflective layer, the same color reproducibility can be obtained in both the transmissive and reflective modes. For example, by making the thickness of the color filter above the openings of the reflective layer twice as large as that of the color filter above the reflective layer, the thickness the light passes through in the color filter is same in both the transmissive and reflective modes and, as a result, the same color reproducibility of the display can be obtained in both modes.
However, in the devices described above, in order to provide the color filter with different thickness between the region above the reflective layer and the region above the openings, the reflective layer must be thicker having a two-layer construction comprised of a resin layer and a reflective layer and, further, two layers of the color filter must be formed. In the case of a three-color filter, in order to form the two layers of the color filter, an exposure and developing process must be repeated six times and, therefore, the manufacturing process becomes complicated and the production cost of the liquid crystal display device itself is increased.